<!DOCTYPE html>
<html>
<head>
	<meta charset="utf-8">
	<title></title>
	<style type="text/css">
		form{
			width: 500px; height: 200px; margin: auto; text-align: center; border: 1px solid;
		}
		input{
			margin-top: 30px;
		}
	</style>
</head>
<body>
	<form action="http://127.0.0.1:8888/logo" method="GET">
		姓名：<input type="text" name="username" id="a1"><br>
		密码：<input type="password" name="password" id="a2"><br>
		<input type="submit" name="提交" id="btn">
	</form>
</body>
<script type="text/javascript" src="jquery-3.0.0.min.js"></script>
<script type="text/javascript">
	$("#btn").click(function(){
		if($("#a1").val("") || $("#a2").val("")){
			alert("不能为空");
			
		}
		

	})
</script>
</html>